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CHEMISTRY
Academician of the Academy of Sciences of the Kazakh SSR M. I. GORYAEV, G. A. TOLSTIKOV, L. A. IGNATOVA,
A. D. DEMBITSKII
ON NATURAL β-CEDRENE
The isolation of β-cedrene from natural sources has not hitherto been described. In the course of studying the chemical composition of the essential oil of hemispherical juniper (Juniperus semiglobosa Rgl.), we established that the sesquiterpene fraction contains cedrol, which is the principal component, and a small amount of hydrocarbons; upon chromatography of these hydrocarbons a fraction with \([\alpha]_{D}^{20} -21.0^\circ\) was isolated. The infrared spectrum of this fraction showed considerable similarity to the spectrum of β-cedrene obtained by us earlier synthetically from α-cedrene \((^{1})\).
More careful chromatography made it possible to isolate β-cedrene with the following constants: \(n_{D}^{20}\) 1.5018; \(d_{4}^{20}\) 0.9330; \([\alpha]_{D}^{20} -2.6^\circ\). The infrared spectra of synthetic and natural samples of β-cedrene practically do not differ from one another (cf. Fig. 1).
Oxidation of synthetic β-cedrene with perbenzoic acid gives the α-oxide, which is so unstable that in the course of isolation it isomerizes to the aldehyde cedranal I. The infrared spectrum of cedranal contains a frequency at 1722 cm\(^{-1}\), and the ultraviolet spectrum of a heptane solution of its 2,4-dinitrophenylhydrazone has a maximum of the long-wavelength absorption band at about 341 mμ. It should be noted that the spectrum of the 2,4-dinitrophenylhydrazone of isocedranone II—the ketone from α-cedrene—has a maximum at about 349.5 mμ. According to a known empirical rule \((^{2})\), the absorption maxima should be located, respectively, at about 337 and 344 mμ. The deviation from the calculated values is probably connected with the presence of a complex tricyclic skeleton. Upon oxidation of natural β-cedrene, cedranal was likewise obtained, identified by the 2,4-dinitrophenylhydrazone with m.p. 195–196°.
Cedranal, synthesized earlier \((^{3})\) by oxidation of primary cedranol III, gave a 2,4-dinitrophenylhydrazone with m.p. 144–144.5°, which is evidently connected with a different orientation of the formyl group. If, upon oxidation of primary cedranol, which most probably \((^{3})\) has an equatorial oxymethyl group, cedranal IV was obtained, then in the isomerization of the α-oxide of β-cedrene it is easy to envisage the formation of isomer I with an axial arrangement of the aldehyde group.
Experimental Part
The essential oil of hemispherical juniper, in an amount of 1.13 kg, was distilled with a Widmer column to remove monoterpenes. The residue (128 g) was poured into 700 ml of 60% methanol; the cedrol (75 g) that precipitated on cooling was filtered off, and the liquid portion was distilled with a Widmer column.
Fig. 1. Infrared spectra: synthetic β-cedrene (1), natural β-cedrene (2), and cedranal (3). (IKS-14, NaCl prism)
The fraction with b.p. 100–124°/2 mm (18.5 g) was chromatographed on 750 g of aluminum oxide (activity II). The product eluted with petroleum ether (8.6 g) was chromatographed on 600 g of aluminum oxide (activity I), with elution by petroleum ether. The first 60 ml of eluate contained 2.19 g of product with \([\alpha]_{D}^{20} -21.0^\circ\).
Repeated chromatography on 400 g of \(\mathrm{Al_2O_3}\) (activity I) gave 0.45 g of β-cedrene, which had the following constants: \(n_{D}^{20}\) 1.5018; \(d_{4}^{20}\) 0.9330; \([\alpha]_{D}^{20} -2.6^\circ\).
Found, %: C 87.90; H 11.75
\(\mathrm{C_{15}H_{24}}\). Calculated, %: C 88.17; H 11.83
Oxidation of β-Cedrene
β-Cedrene (0.35 g) was oxidized with perbenzoic acid in benzene solution at 0° for 16 h. After the usual work-up, 0.30 g of cedranal I was isolated.
On interaction of 0.10 g of cedranal I, 0.1 g of 2,4-dinitrophenylhydrazine, and 0.2 ml of sulfuric acid in a solution of 5 ml of alcohol, 0.15 g of the 2,4-dinitrophenylhydrazone was obtained, m.p. 195–196°. The same product was obtained from synthetic β-cedrene; it gave no melting-point depression in a mixed sample with the hydrazone from natural β-cedrene.
Found, %: N 13.76
\(\mathrm{C_{21}H_{28}O_4N_4}\). Calculated, %: N 13.99
Institute of Chemical Sciences
Academy of Sciences of the Kazakh SSR
Received
28 V 1962
References
- M. I. Goryaev, G. A. Tolstikov, DAN, 139, No. 2, 363 (1961).
- I. N. Nazarov, L. A. Kazitsyna, I. I. Zaretskaya, ZhOKh, 27, 606 (1957).
- M. I. Goryaev, G. A. Tolstikov, Izv. AN KazSSR, Ser. Khim., issue 2 (20), 72 (1961).